The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Engines such as diesel engines and compression ignition engines may produce particulate matter (PM) that is filtered from exhaust gas and collected by a PM filter. The PM filter is disposed in an exhaust system of the engine. The PM filter reduces emissions of PM generated during combustion. Over time, the PM filter becomes full. During a process called regeneration, the PM may be burned within the PM filter.
Regeneration may involve heating the PM filter to a combustion temperature of the PM. Regeneration may be performed using an exhaust heating technique or using an electrical heating technique. The exhaust heating technique refers to the heating of the exhaust gas, for example, by post-combustion injection of fuel. Fuel may be injected into the cylinder during the combustion cycle and after ignition of the air/fuel mixture or into the exhaust stream. When introduced during or after ignition and/or exhaust strokes of the combustion cycle, the injected fuel, referred to as post-injected (PI) fuel, mixes with the exhaust gas and is oxidized by an oxidation catalyst disposed in the exhaust system. The heat released from the reaction in the oxidation catalyst increases the temperature of the exhaust gas flowing through the PM filter, which ignites particulates in the PM filter.
A typical exhaust heating technique may be limited to an exhaust gas temperature that permits slow, controlled burning of the PM. The typical exhaust heating technique may regenerate the PM filter in 20-30 minutes. Exhaust gas temperatures during the typical exhaust heating technique may range from approximately 550° C. to 650° C., depending on the amount of PM in the PM filter. For example only, when the exhaust gas temperature is greater than approximately 650° C. and the PM filter is full, the PM may combust too quickly and release too much heat. The heat may cause thermal stress on the PM filter due to rapid expansion of a substrate of the PM filter. The thermal stress may cause damage to the PM filter. Therefore, the exhaust gas temperature is controlled to be less than a thermal stress temperature, typically less than approximately 650° C.
The electrical heating technique refers to the electrical heating of the exhaust gas entering the PM filter. One or more electrical coils may be disposed upstream from the PM filter and may be activated to heat the exhaust gas. The electrical heating technique provides a quick heating and light-off of the PM. The electrical heating technique may also provide a more uniform and controlled combustion of the PM in the PM filter.